The present invention relates to a liquid for a level or feeler element for the electrical measurement of inclinations and for the determination of the true vertical in the case of stationary bodies and the apparent vertical in the case of moving bodies. In particular, the invention is concerned with a liquid for a feeler element for the determination of the vertical by measuring an electrical current or impedance, respectively between surface electrodes, the electrical current or impedance changing as a function of the tilting, and the electrodes being in contact with the liquid contained in a container and each electrode is coupled with a respective electrode terminal or connection which can be contacted from the outside. Such type of feeler element has been disclosed in the commonly assigned copending U.S. application Ser. No. 526,788 filed Nov. 25, 1974, now abandoned listing as one of the co-inventors Harry Zuest, the inventor of this application, and entitled "Feeler Element For The Electrical Measurement Of Inclinations", the disclosure of which is incorporated herein by reference.
Depending upon the use of the level or feeler element the most different requirements are imposed thereon. Technical data which is particularly to be taken into account and which is in direct relationship with the physical properties of the liquid among other things are: the useful temperature range, which is limited by freezing, boiling, the change in conductivity, the surface tension, the viscosity and so forth; the build-up time of the gas bubble in the feeler element which, at a given temperature, among other things is dependent upon the viscosity and the surface tension; and the impedance or resistance between electrodes which for a given temperature among other things is dependent upon the conductivity of the liquid or electrolyte. Furthermore, the liquid should have storability and stabilty.
Prior art liquids of the type indicated are known which, under standard conditions of use (for instance: room temperature, slow tilting, no jarring during the measurements) satisfy the requirements, to wit: sulfuric acid, ethanol (as taught in U.S. Pat. No. 3,409,993), alcoholic solutions, such as 0.08 grams NaI in 100 ml ethanol (according to U.S. Pat. No. 2,713,726), 0.5 grams NaI in 40 grams methanol (according to German patent publication 1,228,428), 0.02 Moles Mg (NO.sub.3).sub.2.6(H.sub.2 O) in 95% ethanol (according to British Pat. No. 733,973), LiCl in ethanol or isopropanol (according to U.S. Pat. No. 3,497,950), or an iodide in N-butanol (according to U.S. Pat. No. 3,020,506). Further liquids or electrolytes are disclosed in U.S. Pat. Nos. 2,387,313; 2,852,646; 2,932,809; 3,227,984; 3,293,395; 3,293,396 and 3,843,539.
These and similar known liquids possess some drawbacks, e.g. their tendency to electrolytic decomposition and aging thus imposing the use of noble metals as the material of the electrodes, otherwise corrosion effects appear at the electrodes which impair the longevity of the feeler elements. A limitation to the sole use of noble metals is, however, to be avoided; in the case of metallic parts, among other reasons because of costs, in the case of thin films, for instance, as taught in the aforementioned copending, commonly assigned U.S. application Ser. No. 526,788, because of their insufficient adherence.
It is known to suppress the susceptibility to corrosion of metallic parts in contact with aqueous salt-containing solutions by adding to the solution a base. The same holds true for mixtures of water and organic substances as such are used, for instance, in the cooling systems of motor vehicles. It is obvious in the case of the state-of-the-art level liquids to suppress the corrosion of metals in the same manner, i.e. by the addition of substances which act as bases in the solution, where possible with a buffer effect (for instance sodium salts of picric acid or organosiloxane). The result tends to be unsatisfactory. Although it is possible to obtain suitable values for the conductivity and the temperature range, yet it is not possible to adjust the build-up time to that value necessary for fields of application imposing high requirements, for instance for determining the apparent vertical in the case of traveling railroad cars and aircraft, for leveling of aiming or sighting devices on ships and traveling armored vehicles or tanks, and generally for fields of application where shaking or jarring effects must be taken into account.
Another possible measure for preventing corrosion is to use as the solvent a reducing and acid-binding organic liquid. There come under consideration by way of example the following: hydroxyl amines, primary to quaternary alkyl amines and hydroxyl alkyl amines, aromatic amines, and even nitriles, the decomposition of which at the electrodes can act in a manner to bind or neutralize acids. But even here the results are partially unsatisfactory: with the aid of water- and/or alcohol additives it is possible to separately attain acceptable values for the conductivity and the temperature range, but it was not possible to obtain a balance of optimum conductivity, temperature range and build-up times suitable for the aforementioned fields of application. In addition surface tensions obtained in this manner tend to be too low so as to unfavorably affect the shape of the gas bubble and to cause the prolonged adherence of the gas bubble in a previous position.